1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a system and method of managing Temporary Mobile Station Identity (TMSI) parameters in a radio telecommunications network.
2. Description of Related Art
In existing radio telecommunications networks, there is a parameter known as a Temporary Mobile Station Identity (TMSI) which is utilized to identify a mobile station operating within a network. The TMSI is allocated by the network operator. It is advantageous for two reasons to utilize a TMSI to identify a mobile station. First, greater signaling capacity is achieved because the TMSI utilizes fewer bits to identify the mobile station than is utilized by the mobile station's Mobile Identification Number (MIN). For example, in the Digital Advanced Mobile Phone System (D-AMPS), which operates under IS-136, the shortest TMSI is 20 bits long while the MIN is 34 bits in length. This increased signaling capacity is reflected in greater paging capacity as well as reduced overhead and greater payload capacity in each message. The advantage can be illustrated when paging for a mobile station. There are a certain number of time slots that can be utilized, and when using TMSIs to identify mobile stations, up to five mobile stations can be paged in the same slot. When using MINs to identify the mobile stations, however, only three can be paged.
The use of a TMSI also enhances mobile station identification confidentiality. The use of a TMSI makes it more difficult for a fraudulent user to obtain a mobile station's MIN by monitoring broadcast signals. The fraudulent user may obtain the mobile station's TMSI, but the TMSI will probably remain valid for only a short period of time.
The current air interface standard covering the signaling between mobile stations and the network is IS-136. The Intersystem Signaling standard covering the signaling between mobile switching centers (MSCs) is IS-41. The IS-136 air interface standard and the IS-41 Intersystem Signaling standard are hereby incorporated by reference herein. The IS-136 standard, however, has a deficiency regarding the management of TMSIs in the network. Each MSC assigns its own TMSIs to mobile stations operating within the MSC's service area. If a mobile station is assigned a TMSI in a first MSC and then moves into the service area of a second MSC operating with the same System Identity (SID), the mobile station attempts to register in the second MSC utilizing the TMSI assigned by the first MSC. However, the second MSC cannot recognize the TMSI assigned by the first MSC. Therefore, the second MSC cannot identify the mobile station and does not know which HLR to access to retrieve subscriber information. This unsuccessful registration attempt results in a Registration Reject from the second MSC, thereby forcing the mobile station to attempt the registration a second time utilizing its permanent MIN. Thus, there is additional signaling and lost time because the mobile station was not recognized on the first registration attempt in the second MSC.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, two known references discuss subject matter that bears some relation to matters discussed herein. U.S. Pat. No. 5,275,271 to Pfundstein (Pfundstein) discloses a method of structuring a TMSI from a permanent mobile station identity signal (International Mobile Station Identity (IMSI) in the GSM system) to allow fast access to a database. However, Pfundstein does not teach or suggest a solution to the aforementioned deficiency with respect to the management of the TMSI in a network.
A second reference is a standards contribution entitled, "Temporary Mobile Station Identity (TMSI)--Stage 2 Description (rev. 0.3)" from Qualcomm Incorporated (the Contribution). The Contribution proposes a solution to the aforementioned deficiency by passing the mobile station's TMSI from the serving MSC to neighboring MSCs. However, the proposed solution is a complicated scheme in which the network keeps track of each mobile station's TMSI as the mobile station moves from one MSC to another. The Contribution defines the TMSI in such a way that it can be reused by a new serving MSC. However, the Contribution does not just impact the structure of the TMSI. Additional intersystem signaling is required to convey TMSI information from one MSC to another, and to the home location register (HLR).
It is very complicated to maintain a TMSI while a mobile station moves from MSC to MSC. TMSI information must be passed between MSCs, and TMSIs must be structured with prefixes to identify in which MSC the mobile station is operating, etc. Thus, there is adverse impact on the level of required intersystem (IS-41) signaling between MSCs. In order to reuse the TMSI in a new MSC, the Contribution requires a complicated, burdensome scheme which defines neighboring MSCs and requests information from the neighboring MSCs and visitor location registers (VLRs), in order to associate a TMSI with a mobile station and a HLR.
In order to overcome the deficiency in IS-136 and the disadvantages of the solution proposed in the Contribution, it would be advantageous to have a method of managing TMSIs in a radio telecommunications network that does not require a complicated scheme of neighboring MSCs and additional burdensome IS-41 signaling.
Review of each of the foregoing references reveals no disclosure or suggestion of a system or method such as that described and claimed herein.